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Synthesis of Organometallic
Compounds
Advanced Inorganic Chemistry
92/2
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Ruthenium Complexes
• Recently, the chemistry of ruthenium
complexes has been extensively explored.
• less application in organic synthesis than
palladium compounds, probably because
their chemistry is more complicated.
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Ruthenium Complexes
• Ruthenium complexes generally have 5or 6-coordinated geometry and their
oxidation state can vary between -2 to 6.
• This complexity, however, leads to many
interesting reactions and further
developments in this field are expected.
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Ruthenium Complexes
• A wide variety of organoruthenium
complexes is known.
• They can be roughly divided into 4 groups
according to their supporting ligands.
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1. Ru3(CO)12
1. Carbonyl complexes which are generally
derived from Ru3(CO)12.
•
Air stable compound, easy to handle
•
The precursor of an active catalyst for
reduction of nitro groups, C—H bond
activation or carbonylation.
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2. Ruthenium complexes with
tertiary phosphine ligands
• RuCl2L4, RuHClL4, or RuH2L4
• useful for organic synthesis, catalytic
reactions, asymmetric reactions.
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3. Cyclopentadienyl complexes
• Cyclopentadienyl and
pentamethylcyclopentadienyl ligands
effectively stabilize alkyl-ruthenium bonds,
whereas in phosphine complexes the alkyl
group tends to undergo b-hydrogen
elimination.
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Ruthenium complexes having
arenes or dienes
• Low valent ruthenium starting materials via
replacement of arene or diene ligands
• Catalysts for olefin dimerization,
hydrogenation of arenes, or C—C bond
cleavage reaction.
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Preparation of these ruthenium
complexes
• RuCl3.3H2O and Ru3(CO)12
• They are relatively inexpensive and stable
against oxygen.
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Dichlororuthenium Complexes
• RuCl2(PPh3)3
• Coordinatively unsaturated.
• Agostic C-H bond
• A common Ru precursor
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Dichlororuthenium complexes
• Dichlororuthenium complexes are formed by the
reduction of RuCl3.3H2O in the presence of the ligand.
• RuCl2(PPh3)3 is obtained by treatment of RuCl3.3H2O
with an excess of PPh3 in methanol as air-stable shiny
black crystals.
• Reaction of RuCl3.3H2O with PRR’2 or PR2R’ (R = phenyl,
R’ = alkyl) gives cationic dinuclear complexes
[Ru2Cl3(PRnR’3-n)6]Cl under similar conditions.
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RuCl2(PPh3)3
• The X-ray crystallography of RuCl2(PPh3)3
showed that it has a distorted octahedral
geometry with a vacant site which is
occupied by an agostic proton of a phenyl
group.
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Reactivities of RuCl2(PPh3)3
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N-Alkylation of Amines by
Primary Alcohols
• RuCl2(PPh3)3 or RuCl3.3H2O/P(OBu)3
effectively catalyze the N-alkylation of
aromatic amines.
• N-alkylation of aliphatic amines with a
primary alcohol is carried out in high yield
by the use of RuH2(PPh3)4 as catalyst.
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Preparation of heterocycles
N-alkyl piperidine
pyrrolidine
pyrrole
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Oxidation of Amines, Amides,
and Diols
• RuCl2(PPh3)3 is also a catalyst for the
oxidation of nitriles, amides and lactams
under moderate conditions.
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A coordinatively unsaturated 16eruthenium(0) complex
• Reduction of RuCl2(CO)2(PtBu2Me)2 with
magnesium affords an isolable 16e ruthenium(0)
complex Ru(CO)2(PtBu2Me)2.
• Highly reactive toward hydrogen, acetylenes and
phosphines to give coordinatively saturated
complexes.
Trans phosphines
Two COs are bent.
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RuHCl(CO)(PPh3)3
• Formed by the reduction of RuCl3.3H2O with alcohol in
the presence of tertiary phosphines.
• Similarly prepared as Vaska's complex, IrCl(CO)(PPh3)2
• Where does the CO ligand come from?
• Mechansim?
• Stereochemistry: Cl trans to CO
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• Recent developments
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C-H Bond activation
• The generation of coordinatively
unsaturated species play an important role.
• These species are usually produced by
thermal or photo-mediated reductive
elimination of dihydrogen, alkanes,
alkenes or arenes.
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• Mechanistic expect
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Dihydridoruthenium Complexes
• Dihydridoruthenum complexes are reported to
be catalysts for either the direct or transfer
hydrogenation of olefins.
• Ruthenium hydride complexes are also catalysts
for organic reactions such as the coupling
reaction of alkenes with terminal alkynes, the [2
+ 2] cycloaddition of norbornene with alkynes,
Tishchenko-type reactions, and the catalytic
insertion of olefins into the ortho C—H bond of
aromatic ketones.
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Preparation of RuH2(PPh3)4
• RuH2(PPh3)4 is prepared by the reaction of
RuCl2(PPh3)3 with NaBH4 in the presence of PPh3 in
refluxing methanol.
• Or by the direct reaction of RuCl3.3H2O with NaBH4
and PPh3 in refluxing ethanol.
• It is formed as an off-yellow powder and should be
kept under argon, not nitrogen, because a PPh3 ligand
is readily replaced by dinitrogen.
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Reactivities of RuH2(PPh3)4
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Chemoselective aldol reactions
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Coupling reactions of acetylenes
with dienes
• The reaction of l-octyne with 1,3-butadiene
catalyzed by RuH2(PBu3)4 affords 2- dodecen5-yne. A similar coupling reaction is also
catalyzed by RuCl(C5H5)(C8H12).
Mechanism?
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Tishchenko-type dimerization.
• RuH2(PPh3)4 reacts with aldehydes to give esters via
Tishchenko-type dimerization. For example, benzaldehyde is
converted to benzyl benzoate by RuH2(PPh3)4. This reaction
involves C—H bond activation of the formyl proton followed
by formation of a ruthenium acyl alkoxide complex
Ru(OCH2Ph)(COPh)(PPh3)4.
Mechanism?
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RuH2(CO)(PPh3)3 catalyze olefin coupling reactions of aromatic
ketones via C—H bond activation
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A possible intermediate in the
olefin coupling reaction of
aromatic ketone catalyzed by
RuH2(CO)(PPh3)3. Other ligands
are omitted.
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Reactivities of
RuH2(PPh3)4
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Catalytic reactions
Intermediate:
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Ruthenium Complexes with
Chiral Ligand
• the chemistry of ruthenium complexes with the
chiral ligands BINAP and PYBOX are
described.
Atropisomers of the BINAP Ligand
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Ruthenium Complexes Having
Cyclopentadienyl Ligands
• Ruthenocene is relatively un-reactive
• The dinuclear complex [RuCl2(C5Me5)]2 is a versatile reagent.
• prepared by the reaction of RuCl3.3H2O with pentamethylcyclopentadiene in
ethanol
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Treatment of Ru2H4(C5Me5)2 with ethylene results in the formation of a
divinyl(ethylene)diruthenium complex under ambient conditions. This is an
interesting reaction because there are few examples of vinylic C—H bond
activation with metal polyhydride complexes.
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A unique reaction probably proceeds via an acetylide-vinylidene intermediate.
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Ruthenium Complexes with
Arene/Diene Ligands
• Ru(cod)(cot) is prepared by the reduction
of RuCl3.3H2O with zinc powder in the
presence of 1,5-cyclooctadiene in
methanol [192].
It is used in several catalytic reactions and as a
convenient precursor to various zero- or multi-valent
ruthenium complexes
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Reactivities of Ru(cod)(cot)
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• Dimerization of NBD
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For example, ruthenium complexes sometimes show ambiphilic reactivity
allyl carbonate
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• Ruthenium-catalyzed allylations are often
show quite different reactivities and
selectivities from those of palladiumcatalyzed allylations.
The detailed mechanism of the regiocontrolling step is still unclear.
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Useful Ru precursors
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